Efficiency of energy transfer, but not external work, is maximized in stunned myocardium

There is no evidence regarding the effect of stunning on maximization of re gional myocardial external work (EW) or efficiency of energy transfer (EET) in relation to regional afterload (end-systolic stress, sigma(es)). To tha t end, we studied these relationships in both the left anterior descending coronary artery (LADCA) and left circumflex coronary artery regions in anes thetized, open-chest pigs before and after LADCA stunning. In normal myocar dium, EET vs. sigma(es) was maximal at 75.4 (69.7- 81.0)%, whereas EET vs. sigma(es) was submaximal at 12.0 (6.61-17.3) x 10(2) J/m(3). Increasing sig ma(es) increased EW by 18 (10-27)%. Regional myocardial stunning decreased EET (27%) and EW (36%) and caused the myocardium to operate both at maximal EW (EWmax) and at maximal EET (EETmax). EET and EW became also more sensit ive to changes in sigma(es). In the nonstunned region the situation remaine d unchanged. Combining the data from before and after stunning, both EWmax and EETmax displayed a positive relationship with contractility. In conclus ion, the normal regional myocardium operated at maximal EET rather than at maximal EW. Therefore, additional EW could be recruited by increasing regio nal afterload. After myocardial stunning, the myocardium operated at both m aximal EW and maximal EET, at the cost of increased afterload sensitivity. Contractility was a major determinant of this shift.